Trailer shields for welding torches have been used in conjunction with gas shielded welding torches since it was discovered that during the welding process the metal being welded and the hot metal which was just welded reacted with atmospheric gases to weaken or otherwise adversely affect the weld. In use, a trailer shield is attached to the welding torch and is connected to a source of protective gas, such as argon, so that as the torch traverses and welds sections of metal to be joined, the trailer shield follows and covers the freshly welded hot metal with a protective blanket of argon, shielding the hot metal from atmospheric gases. This protection of the hot weld is crucial, as some important structural metals become embrittled or porous if heated beyond a certain temperature while being exposed to atmospheric gases. Titanium, for example, has a high affinity for all elements making up atmospheric gases at temperatures above 1,200.degree. F. While being welded, molten titanium in the wake of the welding torch remains above 1,200.degree. F. for a period of time while it cools from the molten state. If this molten titanium is exposed to atmospheric gases during this time, it becomes glass-like in brittleness, rendering the weld useless. Further, the extent of protection necessary to prevent contamination of the weld is also crucial, with concentrations of atmospheric gases down to 50 to 100 PPM (parts per million) being sufficient to contaminate a weld. Thus, a shield gas must be much denser and heavier (in addition to being non-reactive) than atmospheric gases in order to create an "envelope" around the welding operation and heated metal therefrom within which atmospheric gases are almost totally excluded. Accordingly, trailer shields have been developed for use with various contoured shapes of surfaces to be welded, such as pipes and other curved surfaces, flat surfaces, and surfaces having angled contours, such as when sections of flat plate are to be joined in angular relation. These trailer shields are constructed to closely fit the contours of surfaces to be welded in order to contain the "envelope" of shield gas to the welding operation itself and a region around the welding operation which is heated in excess of potentially damaging temperatures.
Problems with these trailer shields are that because they are rigid, a new trailer shield must be fabricated for each joint configuration or contour of the metals being joined. Further, the shield gas delivered by the trailer shield only covered a hot weld following the welding torch, with the gas from the torch covering the welding operation. Attempts have been made to overcome these problems, and U.S. Pat. No. 2,866,074 (Ronay), filed on Dec. 23, 1958, disclosed one such trailer shield. This trailer shield is constructed having a flexible, corrugated body which can be bent into a variety of configurations to cover various configuration of joints to be welded. This particular trailer shield is provided with a shield gas supply tube having a single outlet which provides shield gas to the interior of the trailer shield at a position nearest the welding torch. An outlet tube positioned at an opposite end of the trailer shield is coupled to a suction apparatus so that shield gas is drawn out of the trailer shield as it is put in. The trailer shield is provided with a clip so that the trailer shield may be clipped to a welding torch, with the torch being provided with a separate supply of shield gas.
Problems with the device disclosed in U.S. Pat. No. 2,866,074 are that shield gas from the welding torch is separated from the interior of the trailer shield, introducing the possibility of weld contamination because of a lack of continuity between shield gas from the torch and shield gas in the trailer shield. Another problem is that since shield gas is actively removed from the trailer shield, the possibility exists that a negative pressure may occur in the trailer shield, allowing atmospheric gases to be drawn into the interior of the trailer shield through clearances between the trailer shield and the welded metal, which could contaminate the weld.
Applicant's invention is directed to a trailer shield in which shield gas from the welding torch is not separated from the interior of the trailer shield. Also, no shielding gas is withdrawn from the present trailer shield, thus providing a slight positive pressure inside the shield and allowing a blanket of shielding gas to cover the weld.
Accordingly, it is an object of this invention to provide a flexible welding torch trailer shield which provides an even covering of shield gas to a hot weld. It is a further object of this invention to incorporate the end of the welding torch into the interior of a trailer shield, and yet another object of this invention is to distribute shield gas ahead of the welding torch to protect an area ahead of the welding torch which becomes preheated due to close proximity of the welding operation.